Centrifugal machine



April 30, 1963 F. P. GOOCH 3,087,621

CENTRIFUGAL MACHINE Filed July 16, 1958 3 Sheets-Sheet 1 Q I p g N 0 8 m INVENTOR.

FRED P. GOOCH ATTORNEY F. P. GOOCH CENTRIFUGAL MACHINE INVENTOR.

FRED P. GOOCH A wa/o a W ATTORNEY April 30, 1963 Fill-8 d July 16, 1958 Fig. 2

April 30, 1963 F. P. GOQCH 3,087,621

CENTRIFUGAL MACHINE 3 Sheets-Sheet 3 Fig. 3

Filed July 16, 1958 INVENTOR. Fig, 3d FRED P. aoocu ATTO RNEY United States Patent 3,087,621 CENTRIFUGAL MACHINE Fred P. Gooch, Pine Ridge, Media, Pa., assignor to The Sharples Corporation, a corporation of Delaware Filed July 16, 1958, Ser. No. 748,898 4 Claims. (Cl. 210-476) 'This invention pertains to centrifugal machines of the type in which liquid and solid material are separated by centrifugal force. The invention pertains more particularly to centrifugal machines of this type that employ perforated rotors or baskets through the walls of which the liquid escapes during its separation from the solid material, and from which the solid material is discharged over a peripheral edge on the rotor.

In prior art centrifugal machines of this type, the rotors are variously shaped, and various forms of impeller mechanism are employed to advance the solid material longitudinally toward the discharge edge for solid material. When the rotor is frusto-conical in shape, such mechanism may function either to advance or .to retard the flow of solid material over the perforated surface of the rotor, depending upon the relation between the angle of repose of the solid material, and the angle between the perforated surface and the axis of rotation.

The flow-control mechanism frequently takes the form of a worm or'screw, a plow, a piston or pusher, or similar device positioned close to the inner perforated surface of the rotor, and movable relative to its perforations. As a result of such relative movement, a grating or comminuting action is set up between the movable member and the perforated surface of the rotor, which tends to reduce the size of the solid particles or crystal moving over the perforated surface, thus producing fines which either escape along with the liquid, or if not, then becoming intermixed with the dried solids of larger particle size, or causing plugging of the perforations.

To overcome these and other shortcomings inherent in centrifugal machines of the prior art, a centrifugal machine embodying a new and distinctly diiferent principle for the advancement and discharge of solids is provided in the present invention, whereby the solid material flows over a perforated rotor surface Without the need of impeller or like mechanism, with the rate of how nevertheless under the positive control of the operator.

Further features of the invention will become apparen to persons skilled in the art as the specification proceeds, and upon reference to the acompanying drawings in which:

FIGURE 1 is an elevation partly in section of a centrifugal machine embodying the invention;

FIGURE 2 is an enlarged view mostly in section of a portion of FIGURE 1;

FIGURE 3 is a sectional elevation, shown broken, illustrlating a different position of the solids discharge mechanism, as well as a modification of the feeding mechanism; and

FIGURE 3a is a fragmentary sectional view illustrating a possible relationship between elements in a further modified form of the apparatus.

Referring now more particularly to FIGURE 1, at is shown a stationary housing. J ournaled in housing 10 is a shaft 11 illustrated as being driven by means of pulleys 12 and belts 13 positioned at one end thereof.

Sccured to the other end of shaft 11 is a perforated rotor 14 of frusto-conioal shape. Means for securing rotor 14 to shaft 11 is illustrated in FIGURE 2, and, as shown, comprises a shoulder 15 on shaft 11, annular rings 16 and 17, which form a labyrinth seal, spacing collar 18,

a collareshaped piston member 21, a second spacing collar 22, and member 23 which threadedly engages the end of shaft 11, rotor 14 being positioned on shaft 11 between collar 22 and member 23. Key 24 prevents relative rotary movement between rotor 14 and shaft 11.

Mounted on shaft 11, and slidable longitudinally with respect thereto, is a perforated frusto-conical member 25 which encloses the periphery of rotor 14, and is of the same general shape. Member 25 is longitudinally movable relative to rotor 14, and rotates therewith. tAIlY means may be employed for the purpose, and as illus trated, rotor 14 is provided with a plurality of studs 26 having extensions 27 which pass through holes 28 in member 25 with a slidable fit.

The means for mounting member 25 on shaft 11 is illustr-ated as including annular members 31 and 32 which are secured together, such as by cap screws 33, to engage the inner edge 34 of member 25. Member 31 is so shaped as to form with .anular member 29 an annular cylinder 35 surrounding annular piston 21. Member 29 is secured to member 31 as by cap screws 30.

Shaft 11 is provided with longitudinal bores or channels 36 and 37' which are connected at one end to fluid pressure lines 38 and 39, respectively, through radial bores or channels 41 and 42 in shaft 11 and channels 43 and 44, respectively, in stationary collar 45 in housing .10. Bores 36 and 3-7 are sealed oif at their other ends, as illustrated at 40.

Bore 36 connects with a radial bore 46 in shaft 11, which leads to a circumferential groove 47 on shaft 11, groove 47 being connected to cylinder 35 on one side of piston 21, through a plurality of circumferentially spaced radial channels in collar 18, one channel being illustrated at 48.

Bore 37, on the other hand, is connected to cylinder 35 on the other side of piston 21, through radial bore 51 in shaft 11, circumferential groove 52 on shaft 11, and a plurality of circumferentially spaced radial channels in collar 22, one such channel being illustrated at 56.

For fluid pressure sealing purposes, tgaskets have been shown at various points throughout the structure illustrated, such as at 54, but since their purpose and function will be well understood by persons skilled in the art, detailed description thereof, in the interest of brevity, will not be made.

As seenin FIGURE 2, member 25 has been moved to the right, this being caused by applying fluid pressure in line 39, fluid pressure in line 38 being released. This in turn applied fluid pressure to the right hand end of cylinder 35, causing member 25 to move to the right, since piston 21 is longitudinally fixed, and member 25 longitudinally movable.

To cause member 25 to move to the left, as seen in FIGURE 2 fluid pressure is applied in line 38', fluid pressure in line 3 9 being released. The result is that fluid pressure is brought to bear in the left-hand end of cylinder 35, which moves member 25 to the left.

Any means known in the art may be employed for alternately applying pressure in one of the fluid lines '38 and 39, while releasing fluid pressure in the other. For purposes of illustration, lines 38 and 39 are shown connected to a four-way valve 55 which is actuated reciprocatingly by a timer 56. Fluid pressure is delivered to valve 55 through line 57 and rotary pump 58 which in turn is connected through line 61 to fluid source 62, such as of oil. Pressure release line 63 connects valve 55 with fluid source 62 for the return of released fluid to source 62.

As illustrated, valve 55 is in a position connecting line 57 to line 39, and line 38 to line 63, the result being that member 25 is in its furthermost position to the right as seen in FIGURE 2. To move member 25 to the left, valve 55 is moved to connect line 57 to line 38, and line 39 to line 63, as will be obvious.

As will be well understood by persons skilled in the art, timer 56 operates valve 55 to alternately supply fluid under pressure to lines 38 and 39, while at the same time releasing pressure in the other of the two lines, thus causing member 25 to reciprocate longitudinally with respect to rotor 14.

Timers of the type shown at 56 are well known. If desired, valve 55 may be operated manually by disconnecting timer 56 from lever 60, and reciprocating said lever 60 by hand.

Returning now to FIGURE 1, it will be noted that member 25 is provided with an annular lip 64 which extends beyond the edge 65 on rotor 14. Edge 66 of annular lip 64 is shown in FIGURE 1 in its position of maximum distance from edge 65 on rotor 14, whereas in FIGURE 3 edge 66 is illustrated in its position of minimum distance from edge 65, these alternate positions of edge 66 with respect to edge 65 being the result of the reciprocating of member 25 relative to rotor 14.

Housing 10 is shown as having a closed end 67 through which extends a stationary feed pipe 68. Feed pipe 68 passes through the center of a frusto-conical feed distributing member 71 which is attached to rotor 14. Another frusto-conical distributing member 72 also is shown attached to rotor 14, feed pipe 68 passing through its central opening 74.

Stationary spray pipe 73 is illustrated as passing through end 67 of housing 10, and through central opening 74 in member 72. Spray head 75 on spray pipe 73 is positioned between member 71 and 72, and may be employed for applying a rinsing spray, if desired, to the solid material passing through rotor 14.

The operation of the new centrifugal machine is as follows:

A slurry, such as of crystals in mother liquor, is fed into the centrifugal machine through line 68, and enters the space or chamber between feed distributing member or wall 71 and rotor 14 wherein it is thrown outwardly by centrifugal force. The slurry passes around, i.e. over, annular edge or dam 76 which projects outwardly from member 71, and slides along perforated surface 77 of rotor 14 toward the larger end thereof, the thickness of the layer of slurry on surface 77 preferably being regulated in any suitable manner, such as by outwardly projecting edges or dams 78 and 79 on distributing members 71 and 72, respectively.

In order that the slurry may be caused to flow outwardly along the inclined perforated surface 77, angle between surface 77 and the axis of rotation should be of a magnitude greater than the angle of repose of the slurry undergoing treatment, it being understood, of course, that the line in FIGURE 1 representing surface 77 falls in a plane which passes through the axis of rotation.

By angle of repose is meant the maximum angle with the horizontal at which an object on an inclined plane will retain its position without tending to slide. In the case of a centrifugal machine the horizontal becomes the axis of rotation whether it is horizontal, vertical, or at some other angle. The term angle of repose is also used with the related meaning of the maximum angle with the horizontal (or axis of rotation) at which loose material, such as crystals, comminuted coal, or other finely or coarsely divided material, will retain its position without tending to slide. It is, of course, recognized that the moisture content, and the distribution of fine and coarse particle, have an effect on the value of this angle, as is well understood by persons skilled in the art. Generally speaking, the angle of repose of solid particles decreases with decrease in moisture content.

With the perforated surface 77 positioned at an angle with respect to the axis of rotation which is greater than the angle of repose of the slurry in its various states during the treatment, including, of course, that of the dried solids, the slurry slides along perforated surface 77 toward the discharge end of rotor 14, being separated from liquid as it progresses. Since the rate of free travel of the slurry along surface 77 increases with increase in centrifugal force, and since the purpose of centrifuging is to apply centrifugal forces which are many times the force of gravity, it is found that when the angle 0 is greater than the angle of repose of the material in its various states while undergoing treatment, the material will pass through the rotor at a rate far too high for practicable separation purposes. Fow retarding mechanism is, therefore, an essential In the prior art the necessary retarding action is accomplished either by making angle 0 less than the angle of repose, and resorting to impeller mechanism to advance the solids, or by making angle 0 greater than angle of repose, and resorting to a member similar to an impeller, such as for example, a scroll or screw, but which performs the reverse function of retarding the rate of flow of solids over the perforated surface. Both arrangements suffer from the shortcomings pointed out above.

In the present invention the rate of flow of the slurry across the reticulated frusto-conical peripheral wall 77 is controlled through the reciprocation of annular lip 64, thus avoiding the mechanical grinding action of impeller or retarding mechanism functioning in association with the perforated surface. Annular 'lip 64 is preferably imperforate, although it may take the form of a screen or the like for additional draining purposes.

The solids sliding down perforated surface 77 eventual- 1y reach edge 65 of rotor 14, at which point the solids pass around, i.e. over, outwardly projecting edge or dam 81 on distributing member 72, and then onto the inner surface of annular member or lip 64.

Annular lip 64 is shown for purposes of illustration as having an inner surface which is more or less parallel to the axis of rotation, and of a width such that the angle a between line 85, drawn parallel to the axis of rotation, and line 86 which touches edge 66 and the outer edge of dam 81, (both lines being in a plane passing through the axis of rotation), is less than the angle of repose of the discharging solids. As a consequence the fiow of solids stops, and if annular edge 66 were to continue to occupy its position as illustrated in FIGURE 1, no solids would be discharged over edge 66, the solids simply accumulating in rotor 14 to eventually stop the feed through pipe 68. The angle between line 86 and the axis of rotation is, of course, the same as angle a.

It will be recalled that annular edge 66 is illustrated in FIGURE 1 as occupying its position of maximum distance from edge 65 on rotor 14. In one type of operation, when annular edge 66 is moved to its position of minimum distance from edge 65 as illustrated in FIG- URE 3, the angle illustrated in FIGURE 3 by the letter b is still less than the angle of repose of the discharging solids, for it is not necessary, for purposes of discharging solids from rotor '14, to move lip 64 to a position where the angle b equals or exceeds the angle of repose of the solids. This is because when lip 64 is moved to the left from the position shown in FIGURE 1, it slides out from under solids deposited thereon. Since such solids, due to friction, move only slightly but not appreciably to the left, which is actually uphill, any desired quantity thereof may be caused to discharge over edge 66, the amount increasing with the distance that edge 66 is moved to the left. When lip 64 is returned to its original position to the right, such discharged solids are replaced by flow of further solids from rotor 14, which is actually downhill, friction between the solids and lip 64 assisting in the forward movement of solids. Short frequent reciprocating movements of this character, such as at a rate between 20 and 200 times per minute, are found to be preferable to longer less frequent reciproating movements, for the former make it possible to more nearly simulate continuous movement of solids through the rotor.

Lip 64 may be of any desired greater width, and the solids need not necessarily be discharged over edge 66 as the result of a single reciprocation at the beginning of operations, for they in any event will eventually reach edge .66 due to the incremental advance resulting from each reciprocation cycle, thereafter to be discharged over edge 66 with each reciprocation.

Thus as a result of the reciprocation of reticulated member 25, to which annular lip 64 is attached, solids are discharged intermittently at any desired frequency from the rotor '14. Discharged solids are collected in housing and are removed therefrom through chute 82. Liquid passing through perforated surface 77 of rotor 14 passes through the perforations shown at 83 in member 25, and is withdrawn from housing 10 through chute 84.

In another type of operation of the centrifugal machine of the invention, dimensional changes to the casing, reciprocating means, etc. which will be obvious to one skilled in the art, permit annular edge 66 to be moved to a positionof minimum distance from edge 65' so that the angle 11' having a ray tangent to edge 66 and the edge of dam 81' (FIG. 30) becomes greater than the angle of repose of the discharging solids. This causes all of the solids in the rotor 14 to be discharged therefrom at one time, particularly if suitably dried, and adapts the invention for cyclic operation, for example, in the following manner.

With annular lip 64 in its outer position such as shown in FIGURE 1, rotor 14 is charged with a slurry, the feed being discontinued after charging. After the solids have been suitably centrifuged for separation of liquid therefrom, annular lip- 64 is moved into a position as shown in FIGURE 3a whereat the angle illustrated at b is greater than the angle of repose of the dried solids. The entire contents of rotor 14 are thus discharged there from, and are removed from the housing, separately from the liquid, through segregated chutes comparable to chutes 82 and 8-4 of the FIGURE 1 representation. Annular lip 64 is now returned to its original position such as illustrated in FIGURE 1, whereupon rotor 14' is recharged with solids by opening a valve (not shown) comparable to valve 90, and the cycle repeated.

Various other steps may be introduced into the cycle, as is common in the cyclic operation of centrifugal machines, for instance, as described in US. Patents 2,271,- 493, 2,566,174, and 2,658,620.

Moreover, cyclic operation of the centrifugal machine of the invention lends itself to automatic control such as described in the foregoing patents.

It will be understood that in the first type of operation above described in which angle b does not exceed the angle of repose of solids discharging from rotor 14, irrespective of the position of annular lip 64, valve 90 normally will be continuously in open position.

While dam 8:1 is shown near the discharge end of rotor 14, which is preferred, it obviously may occupy any other position between the inlet and outlet of rotor 14, if desired for any reason, having in mind what has been said above with respect to angles a and b, darn 81, of course, being the outermost dam functioning in conjunction with lip 64. The same applies to the spacing between dam 81 and the inner periphery of the rotor, which may be as desired, although a relatively thin layer of solids in rotor '14 is usually preferred. Dams 76, 7-8 and 79 also regulate cake thickness, as will be obvious.

On the other hand, it is to be understood that the various dams, including dam 81, may be dispensed with, if regulation of cake thickness, and a restricted width of annular member or lip 64 are not desired in the design of the centrifugal machine. For example, angle 0 may be made only slightly larger than the angle of repose of the particular slurry being treated, and lip 64 parallel to the axis and of sufficient width to avoid discharge of solids when in its outermost position, thus eliminating dam 81, without departing from the spirit of the invention. It is preferred, however, to build the centrifugal machine with an angle c of sufficient size for the treatment of a large variety of slurries, for example, of 35 and to employ a dam 81 so that the width of lip 64 may be held to a restricted width but sufficient for the controlled discharge of a wide variety of solids, it being understood, how-ever, that lip 64 may be of any desired greater width, as pointed out above.

A modification of the feeding mechanism is illustrated in FIGURE 3, wherein a stationary feed distributing member or wall 91 mounted on the end of feed pipe 68 is substituted for a rotary feed distributing member, such as member 71. The use of a stationary feed distributing members, such as member 91, is found advantageous in certain instances, for example, when a slurry is sticky in character, in that a somewhat better distribution of the solids on the periphery of rotor 14 is obtained.

Also the radius of member 71, or of member -91, may be decreased or increased to decrease or increase, respectively, the centrifugal head at edge or dam 76, as will b understood, the shape of the rotor being made to conform, if necessary, to obtain the desired spacing between dam 76 and surface 77. In larger and/or high-speed machines, it may be desirable to limit the centrifugal head at edge or point 76.

Usually, the hydrostatic pressure on the feed in pipe 68 is preferably held more or less constant and of nominal value, e.g, 5 or 6 feet, although, if desired, one or both may be departed from without departing from the spirit of the invention. A constant-head overflow device, for example, may be employed.

It will, of course, be understood that any other means may be provided for reciprocating annular lip 64, accomplishing this purpose through a member 25 being merely illustrative. Moreover, it will be understood by persons skilled in the art that since the function of reciprocating member 25 is merely to reciprocate lip, ,64, member 25 may have any other desired configuration and construction. Also it will be understood that any other means may be employed for reciprocating member 25, the use of hydraulic means being illustrative.

For purposes of convenience in description, the periphery of rotor 14 has been shown with a plurality of closely spaced passages or holes of relatively small diameter, simulating a screen. It will, of course, be understood by persons skilled in the construction of centrifuges, that any other form of reticulated or liquid pervious surface may be substituted, for a rather wide variety are Well known in the centrifuging art. Thus the term reticulated, as used in the claims, is intended to define any type of construction which is pervious to liquid, that is which is capable of permitting liquid to pass therethrough while retaining solids, irrespective of its construction. The same applies to member 25 as will be obvious.

It will, of course, be understood that various refinements may be added, such as resilient bumper stops, e.g. of springs, rubber, or the like, to cushion the stopping of member 25 at each end of its reciprocating movement. Also it will be understood that the inner surface of annular lip 64 need not be parallel to the axis of rotatron, but may form any other angle as long as angle a reingins less than the angle of repose of the discharging s01 s.

Typical of crystals, or other solids, which may be dried, dehydrated and/or separated from mother liquor, in the apparatus of this invention, are the following: 'acetylsalicylic acid, ammonium persulphate, ammonium sulphate, borax, boric acid, copper sulphate, ferrous sulphate, hexarnine, monochloracetic acid, naphthalene, paradichlorobenzene, polystyrene, potassium chloride, sodium bicarbonate, sodium carbonate, sodium chlorate, sodium chloride, sodium hydrosulphite, sodium sesquicarbonate, sodium sulphate, urea, zinc sulphate, coal, starch fiber and reclaimed rubber.

Having particularly described the invention, it is to be understood that this is by way of illustration, and that changes, omissions, additions, substitutions, and/or other modifications may be made without departing from the spirit thereof. Accordingly it is intended that the patent shall cover, by suitable expression in the claims, the various features of patentable novelty that reside in the invention.

I claim:

1. A centrifugal machine including a rotor with a single reticulated frusto-conical peripheral wall having a discharge outlet for solid material at its larger end, said wall terminating at its said larger end means to rotate said rotor, a feed distributing member positioned within the smaller end of said peripheral wall, means for feeding a slurry of liquid and solids into said centrifugal ma chine centrally of said distributing member, a darn POSl-z tioned within said peripheral wall and adjacent said discharge outlet, said dam having a circular outer edge spaced from the inner surface of said wall, an imperiorate annular end member positioned closely about and extending axially outwardly beyond said discharge outlet, means for rotating said annular end member with said rotor, means for continually reciprocating said annular end member axially relative to said discharge out:- let, the inner surface of said peripheral wall defining an angle with the axis of rotation in a plane of said axis; which is greater than the original angle of repose of said slurry and of said solids, and an imaginary straight line in a plane of the axis of rotation and touching the inner edge of the outer periphery of said annular end member when in outermost position and the outer edge of said dam defining an angle with the axis of rotation which is less than the angle of repose of the discharging solids.

2. The centrifugal machine of claim 1 having at least, one additional dam between the dam of claim 1 and the distributing member.

3. The centrifugal machine of claim 1 wherein an imaginary straight line touching the inner edge of the outer periphery of said annular end member when in innermost position and the outer edge of said dam defines an angle with the axis of rotation which is less than the angle of repose of the discharging solids.

4. A centrifugal machine including a rotor with a single reticulated frusto-conical peripheral wall having a discharge outlet for solid material at its larger end, said wall terminating at its said large end, means to rotate said rotor, a feed distributing member'positioned within the smaller end of said peripheral wall, means for feeding a slurry of liquid and solids into said centrifugal machine centrally of said distributing member, a dam of lesser radius than the larger end of said peripheral wall and positioned within said peripheral wall adjacent said discharge outlet, said darn having a circular outer edge spaced from the inner surface of said wall, an imperforate annular end member positioned closely about and extending axially outward beyond said discharge outlet, means for rotating said annular end member with said rotor, means for reciprocating said annular eud member axially relative to said discharge outlet, the inner surface of said peripheral wall defining an angle with the axis of rotation in a plane of said axis which is greater than the original angle of repose of said slurry and of said solids, and an imaginary line in a plane of the axis of rotation and touching the inner edge of the outer periphery of said annular end member when in outermost position and the outer edge of said dam and defining an angle with the axis of rotation which is less than the angle of repose of the discharging solids, the imaginary line defining an angle greater than the angle of repose of the discharging solids when said annular end member is in innermost position.

References Cited in the file of this patent UNITED STATES PATENTS 571,912 Abell Nov. 24, 1896 1,342,743 Elmore June 8, 1920 2,315,036 Bailly Mar. 30, 1943 2,755,934 Ruegg July 24, 1956 2,828,021 Ruegg Mar. 25, 1958 2,982,411 Fontein May 2, 1961 FOREIGN PATENTS 22,190 Great Britain 1912 34,197 Austria Aug. 25, 1908 217,585 Germany Jan. 5, 1910 

4. A CENTRIFUGAL MACHINE INCLUDING A ROTOR WITH A SINGLE RETICULATED FRUSTO-CONICAL PERIPHERAL WALL HAVING A DISCHARGE OUTLET FOR SOLID MATERIAL AT ITS LARGER END, SAID WALL TERMINATING AT ITS SAID LARGE END, MEANS TO ROTATE SAID ROTOR, A FEED DISTRIBUTING MEMBER POSITIONED WITHIN THE SMALLER END OF SAID PERIPHERAL WALL, MEANS FOR FEEDING A SLURRY OF LIQUID AND SOLIDS INTO SAID CENTRIFUGAL MACHINE CENTRALLY OF SAID DISTRIBUTING MEMBER, A DAM OF LESSER RADIUS THAN THE LARGER END OF SAID PERIPHERAL WALL AND POSITIONED WITHIN SAID PERIPHERAL WALL ADJACENT SAID DISCHARGE OUTLET, SAID DAM HAVING A CIRCULAR OUTER EDGE SPACED FROM THE INNER SURFACE OF SAID WALL, AN IMPERFORATE ANNULAR END MEMBER POSITIONED CLOSELY ABOUT AND EXTENDING AXIALLY OUTWARD BEYOND SAID DISCHARGE OUTLET, MEANS FOR ROTATING SAID ANNULAR END MEMBER WITH SAID ROTOR, MEANS FOR RECIPROCATING SAID ANNULAR END MEMBER AXIALLY RELATIVE TO SAID DISCHARGE OUTLET, THE INNER SURFACE OF SAID PERIPHERAL WALL DEFINING AN ANGLE WITH THE AXIS OF ROTATION IN A PLANE OF SAID AXIS WHICH IS GREATER THAN THE ORIGINAL ANGLE OF REPOSE OF SAID SLURRY AND OF SAID SOLIDS, AN AN IMAGINARY LINE IN A PLANE OF THE AXIS OF ROTATION AND TOUCHING THE INNER EDGE OF THE OUTER PERIPHERY OF SAID ANNULAR END MEMBER WHEN IN OUTERMOST POSITION AND THE OUTER EDGE OF SAID DAM AND DEFINING AN ANGLE WITH THE AXIS OF ROTATION WHICH IS LESS THAN THE ANGLE OF REPOSE OF THE DISCHARGING SOLIDS, THE IMAGINARY LINE DEFINING AN ANGLE GREATER THAN THE ANGLE OF REPOSE OF THE DISCHARGING SOLIDS WHEN SAID ANNULAR END MEMBER IS IN INNERMOST POSITION. 